Blood Alcohol Calculator (BAC)

The Widmark formula, developed in the 1930s and still used in forensic toxicology, estimates blood alcohol concentration from the pure alcohol consumed, body weight and a distribution factor (r = 0.68 for men, 0.55 for women, reflecting body-water share). This calculator counts one US standard drink as 14 grams of pure alcohol — roughly a 355 ml beer at 5%, 150 ml wine at 12%, or 44 ml spirits at 40% — and subtracts elimination at 0.015% per hour.

BAC estimates are rough: food, medications, pour sizes and individual metabolism shift real values widely, and any amount of alcohol impairs driving. Never use this calculator to decide you are safe to drive — if you have been drinking, do not drive. Educational information only, not medical or legal advice.

The formula

Widmark: BAC% = alcohol (g) ÷ (weight (kg) × r × 10) − 0.015 × hours, floored at 0 (r = 0.68 men, 0.55 women)

Worked example

Four standard drinks (56 g of alcohol) in an 80 kg man give a Widmark BAC of about 0.088% after one hour — above the 0.08% driving limit used in most of the US.

The example is pre-loaded in the result panel — press Calculate with your own numbers to replace it.

Frequently asked questions

Why do women reach a higher BAC from the same drinks?

The distribution factor r is lower (0.55 vs 0.68) because women on average carry a higher share of body fat and less body water, so the same alcohol dose concentrates in a smaller fluid volume.

How fast does BAC fall?

The liver eliminates alcohol at a roughly constant rate, modelled here as 0.015% per hour (observed range about 0.010–0.020). Coffee, food after the fact and fresh air do not speed it up — only time does.

What is the legal driving limit?

0.08% in most US states (0.05% in Utah), 0.05% in most of Europe and Australia, and lower or zero for novice and commercial drivers in many places. Impairment begins well below any limit.

Category: Health & Fitness calculators